I. Field of the Invention
This invention relates to a rotatable handgrip actuating system for use with a Bowden tube (cable within a tube) type motion translation system. More particularly, it relates to a rotatable handgrip actuating system for use in operating a derailleur cable on a bicycle.
II. Description of Related Art Including Information disclosed Under 37 CFR Secs. 1.97 & 1.98
One type of, shift actuator that is conveniently rotatable mounted on a handlebar and positioned so as not the require the rider to remove a hand or even a thumb to operate the actuator is disclosed in U.S. Pat. No. 4,900,291 issued Feb. 13, 1990 to one of the co-inventors of this application and assigned to the assignee of this application. U.S. Pat. No. 4,938,733 issued Jul. 3, 1990 to the same co-inventor of this application and assigned to the assignee of this application, discloses a modification of the shift actuator of the prior patent.
Another type of bicycle derailleur cable actuating system which is of the same general type as that of this invention is disclosed in U.S. Pat. No. 5,102,372 issued Apr. 7, 1992 to three of the co-inventors of this application and also assigned to the assignee of this application. To further match the mechanical operating characteristics of a twist grip cable actuating system with the relative cable movement and force requirements of a bicycle derailleur system, U.S. Pat. No. 5,197,927 issued Mar. 30, 1993 reveals the use of a "shovel cam" in combination with a "jack spool". This later patent issued to the same three inventors as the prior patent and again, is assigned to the assignee of this application. For the purpose of providing a full teaching of the construction and operating requirements of a bicycle derailleur-type shifting system, and particularly ones operated by a twist grip actuating system, the above-mentioned patents are incorporated herein by reference.
In general, twist grip cable pulling devices for controlling bicycle derailleurs are mounted on the handlebar. Thus, the handlebar diameter presents a practical limit on the minimum spooling radius of the twist grip control. As set forth above, and as described in detail in the above-mentioned patents, derailleurs may require a particular cable tension for actuating each different derailleur actuation step. The tension required may vary within the range of desired derailleur position settings. However, there is a practical limit to the maximum torque which is comfortably exerted on a twist grip by the typical human hand. Therefore, it is desirable to not only vary the mechanical advantage of the twist grip control, but also to maximize the mechanical advantage, that is to minimize the spool radius, corresponding to certain derailleur position settings.
Previous twist-grip designs such as that disclosed in U.S. Pat. No. 5,134,897, issued Aug. 4, 1992 and assigned to Campagnolo sought to minimize the spool radius by mounting the twist grip directly over the handlebar. However, this has proven to be undesirable in certain situations, such as in off the road riding, because abrasive dirt and mud can easily find its way between the often thin walled handlebar and the typically plastic twist grip. The abrasive material tends to stick to the plastic and then abrade the thin walled metal handle bar, which in light weight bicycles are frequently formed of a relatively soft metal like aluminum.
Other designs such as one marketed by Suntour avoided the twist grip/handlebar interaction by mounting a stationary tube or mandrel on the handlebar over which the twist grip rotates. The thickness of the mandrel adds to the spooling radius which, in the case of the Suntour design, necessitates the use of a separate jackshaft carrying more spools so as to gain the required mechanical advantage for actuating the derailleur control cable. This Suntour design is shown in published patent application WO93/18960 which is based on PCT/JP93/00335.